Just kicking around the idea.. All input is welcome.
Here is where I'm at: REBAR for the shaft.. Maybe weld a carbide bit to the rebar and drill at 12' sections? Weld sticks together as needed - making length as you drill deeper and deeper.

Good thing I drank all my coffee or it would be all over my computer screen. Mike has put forth a few hair-brained ideas before and this is one of them.

The mass of a drill bit 100 feet long is more than any 1/2 inch hand drill could drive. I used to work on big drill rigs and know what sort of power it takes. Also, it takes a lot to lift out 100 feet of drill steel.

REBAR is solid. You need something that is hollow to run air/water/slurry down. The water is required to carry up the drill cuttings. Drill rigs usually mix up a slurry that is much heavier than water and so will float the cuttings which are relatively lighter in the heavy slurry.

12 foot sections would require that you have staging 12 feet high either movable or with multiple levels to stand on.

Unless the bedrock is exposed, you first need to drill through the overburden and case it out. You also need to seal the casing into the bedrock.

Getting through the 20' of overburden is the easy part.. I can easily wash down a 2" PVC pipe.. Then there is the SW Florida coral rock ( coquina ) that needs to be drilled through. As you probably already know its calcium carbonate based and not very hard to bore a hole through. The weight of a rebar shaft / bit assembly can easily be overcome with a 4" x 4" gantry type set-up with pulleys. They also sell some high quality hammer drills out there that could make small work of calcium carbonate shell bedrock. Any ideas on a steel shaft that is readily available cheaply? 1/2 steel round? The objective with this post is to determine if something like this can be undertaken based on readily available items. Naysayers, go beat meat in some other forum.. I am only interested creative ideas from creative brains

Allright here it goes then, you cannot use a 1/2" concrete drill, as you said you are in need of creative ideas from creative brains (so you might just want to switch yours of). Use a gas drive auger. The problem with using a normal concrete bit is that it is hardened steel, have fun welding extensions to it they are simply just going to snap of right at the welds every time. You will need to fashion a bit of mild steel and heat treat after you have fashioned a way of securing to your drill stem. I would use 1" sched 40 steel pipe as drill stem. have fun...

The weight of a rebar shaft / bit assembly can easily be overcome with a 4" x 4" gantry type set-up with pulleys. They also sell some high quality hammer drills out there that could make small work of calcium carbonate shell bedrock.

Click to expand...

That still does nothing to reduce the mass. What hammer drill do you think will move the mass of 100 feet of drill steel? A tiny little hammer inside the drill won't telegraph down to the drill bit because of the mass. As I said, I worked on drill rigs and know what it takes.

OK Guys, don't knock what you haven't done! I teach water well drilling internationally and we do what they say can't be done because we have too! I would change my thinking to cable tool drilling. Meaning using a heavy steel bar that will just fit inside the 2" PVC. The steel bar needs to be 10 to 150 pounds in weight and hardened to a blunt chisel on the bottom end (like a star drill concrete bit). Attach this to a cable (or rope), run the cable through a tri-pod and sheve at the top. Put five gallons or less water in the hole, raise and drop the steel bar six to 18 inches and drop it into the coral (lime rock)rock. Continuine doing this beating the rock into a mud. Then run a small bailer in the hole and bail out the mud, then repeat the process until you reach the depth that you want to go. This is a very slow but capable method of drilling rock. It's an old method that is still used today. . . but it is slow and labor intensive. http://www.youtube.com/watch?v=H6N0x8BnOKE.

So, every 4 feet you need to trip out all the drill steel that according to the OP, he welded together. Then bail it out and weld the drill steel back together to resume drilling. I do realize that you propose using steel cable to avoid all the welding/rewelding.

I'm surprised you can even go 4 feet in one round. In my experience in rotary drilling, if the air/water/slurry was ever stopped for 4 feet, the drill steel might never come back out and that'd get you fired. I was on one job where the previous driller not only jammed the drill steel but also drove the clay slurry up into the air motor of the hammer.

I'm not sure what he is conspiring to do is even legal in the state of Florida. He risks contaminating the aquifer by not properly sealing the casing into the bedrock possibly allowing surface water to leak in.